The present invention relates to high temperature resistant polymerizable metal oxide particles, to processes for preparing them, to compositions comprising said particles, and to their use.
Nanoscale inorganic materials (materials having an average article size in the nanometer range) with surface modification by organic radicals are already known; see the prior art discussed in more detail below. The known nanoscale materials, including the preparation processes, have a number of disadvantages which restrict their use almost exclusively to the application of hard layers to substrate surfaces. The reasons for these disadvantages lie predominantly in the preparation of the materials by the sol-gel process. The sol-gel process is described, for example, in C. J. Brinker and G. Scherer xe2x80x9cSol-Gel-Sciencexe2x80x94The Physics and Chemistry of Sol-Gel-Processingxe2x80x9d, Academic Press, New York (1989), and also in DE 1941191 A, DE 3719339 A and DE 4020316 A. In the sol-gel process, inorganic particles, such as aqueous colloidal silicon dioxide solutions (water glass), are reacted with alkoxysilanes via hydrolysis and condensation reactions, giving gels having different or even divergent properties.
The properties of the particles obtained by the sol-gel process may be altered by modifying the surface. The reaction of colloidal silicon dioxide by the sol-gel process with acrylated alkoxysilanes in an inert organic solvent, and the use of the resulting products to produce scratch resistant coatings, for instance, have already been described; see, for example, U.S. Pat. No. 4,455,205, U.S. Pat. No. 4,478,876, and Proceedings RadTech, North America ""92, pages 457-461 (1992). A similar procedure has been taken for the introduction of functional groups into radiation curable sol-gel coatings; see New J. Chem. 18, 1117-1123 (1994) and DE 4338361 A. Furthermore, Chem. Mater. 9, 1562-1569 (1967) describes the modification of colloidal silicon dioxide with a trialkoxysilane containing epoxy or 1-propenyl ether groups, in anhydrous, liquid organic phase.
The particles prepared by the sol-gel process possess the following disadvantages:
They lack reproducible structures and properties.
Their preparation is costly and not always environment-friendly.
The storage stabilities are unsatisfactory.
There are no possibilities, or only limited possibilities, for their copolymerization with other monomers.
The amount of particles which may be taken up into substrates, such as coating materials, etc., is limited.
The use of the particles obtained by the sol-gel process is therefore limited in practice to the production of hard, scratch resistant coatings.
It is now an object of the present invention to provide particles and processes for their preparation which do not have at least one of the abovementioned disadvantages. In particular, the intention is to provide particles which are simpler and more economic to prepare and which are also suitable for high temperature application.
It has surprisingly now been found that this object is achieved if the particles are prepared by a process in which the starting material is not a sol but instead the particles are used as solids and the surface is modified and covalently bonded by reaction with appropriate reagents.
The present invention accordingly provides high temperature resistant polymerizable metal oxide particles having a glass transition temperature of the homopolymers of xe2x89xa7100xc2x0 C. and having a core A comprising at least one oxide of a metal or semimetal from main groups three to six, transition groups one to eight of the periodic system, or the lanthanides and having at least one group xe2x80x94(B)w, xe2x80x94X, which is bonded covalently to the core by way of one or more oxygen atoms of the oxide or hydroxide, w being 0 or 1 and B being a radical of the formulae
xe2x80x94(MeO)xMe(O)y1xe2x80x94(R)y2xe2x80x94 or xe2x80x94R(O)zxe2x80x94
in which x is from 0 to 100, y1, y2 and z independently of one another are 0 or 1, and Me is a metal or semimetal from main groups three to six or transition groups three to eight of the periodic system, the free valances of Me representing a bond to a further oxygen atom of the core A and/or a bond via an oxygen atom to an Me in another group B or and/or a bond to an oxygen atom of another core A and/or being satisfied by H, an organic radical and/or a trialkylsilyloxy radical;
R is divalent alkyl, cycloalkyl, aryl, arylalkyl, alkylaryl, alkoxy, acyl, acyloxy or a radical remaining following the removal of two phenolic hydrogen atoms from a phenol compound having at least two phenolic hydroxyl groups, it being possible for R to be substituted, if desired, by 1, 2 or 3 radicals selected independently of one another from hydroxy, alkoxy, halogen and also, in the case of aryl or cycloalkyl radicals, alkyl, and/or interrupted in the chain by one or two oxygen atoms, and
X is a reactive functional group or a radical containing a reactive functional group.
The invention further relates to a process for preparing the high temperature resistant, polymerizable metal oxide particles, in which the radicals B, Bxe2x80x94X or X are covalently bonded to the core A, present in solid form, in the presence of a strong acid.